SB 761 

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Copy 1 



OF THE PRINCIPAL INSECT ENEMIES OF ' 
FORESTS IN THE UNITED STATES. 



A. D. HOPKINS. Ph. P.. 

In Charge of Forest Insect Investigations, Division of Entomology. 



[Reprint from Yearbook of Department of Agriculture for 1902.] 



lliGEOLOGICALSIVEK 
JUN 16 1904 
LIBRARY. 



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CONTENTS. 



Page. 

Introduction 265 

The spruce-destroying beetle 266 

Description of the various stages of the beetle _ 266 

Habits of the adult and larva 267 

Methods of preventing losses from future depredations 269 

The destructive pine-bark beetle 270 

1 description of the various stages of the beetle 270 

Habits of the adult and larva 271 

Probable beginning of a new invasion in the South 273 

Evidence of an old invasion in Texas 273 

Methods of preventing destructive invasions 273 

Trapping the beetle and its 1 »ro< >ds 275 

The pine-destr< rying beetle of the Black Hills 275 

Description of the 1 >eetle and its work 275 

Characteristic features of the infested ami dead timber. 279 

Methods of combating the pest 280 

Other destructive species of Dendroctonus 281 

Summary 281 

General recommendations 282 

in 



ILLUSTRATIONS. 



PLATES. 

Page. 

Plate XXVIII. Work of the spruce-destroying beetle 266 

XXIX. Work of the pine-destroying beetle of the Black Hill? 280 

TEXT FIGURES. 

Fig. 23. Spruce-destroying beetle 267 

24. Work of the spruce-destroying beetle 268 

25. Different methods of girdling trees 269 

26. I >estructive pine bark-beetle 270 

27. Work of destructive pine-bark beetle 271 

28. The pine-destroying beetle of the Black Hills 276 

29. Larva of the pine-destroying beetle of the Black Hills 276 

30. Pupa of the pine-destroying beetle of the Black Hills 276 

31. Work of the pine-destroying lieetle of the Black Hills (chambers) . . . 277 
o2. Work of the pine-destroying beetle of the Black Hills (pitch tubes 

on surface of bark ) 278 

v 



SOME OF THE PRINCIPAL INSECT ENEMIES OF CONIF- 
EROUS FORESTS IN THE UNITED STATES. 

By A. I). Hopkins, Ph. D., 
In Charge of Forest Insert Investigations, Division of Entomology. 

INTRODUCTION. 

Within recent years the writer has made a preliminary survey of 
the principal forest regions of the United States, from southeastern 
Florida to northwestern Washington, from northern Maine to eastern 
Texas, and in the middle Appalachian region, the middle Rockies, and 
the Pacific slope, for the purpose of obtaining information relating- to 
the principal enemies of the forests, the location and extent of areas 
of greatest depredation, and the possibilities of preventing losses. 

It was found that among the many hundreds of insect enemies of 
forest trees observed and collected there are a few species which are 
of primary importance in their relation to widespread devastations. 
Indeed, it would seem that the most important enemies of coniferous 
forests in this country are restricted to a few species of a single genus 
of beetles. This genus was described by Erichson, of Berlin, Ger- 
many, in 1836, under the name Dendroctonus, which means '"killer of 
trees." It is represented in Europe by only a single species, but in 
this country some eighteen species have been recognized. With few 
exceptions, they are all that the generic name implies, and the greater 
number are even more, for they are real devastators of forests. 

One of the species of this genus, known as the spruce-destroying 
beetle, has been, according to published data, a menace to the Northern 
spruce forests during the past eighty years. Its work has from time 
to time taken the character of an invasion and destroyed many mil- 
lions of dollars 1 worth of the best spruce timber in different sections, 
from New Brunswick to New York. 

The destructive pine bark-beetle is another species which threatened 
the entire destruction of the pine and spruce of Virginia and West 
Virginia between 1890 and 1892, and before its ravages were checked 
it killed many millions of the best pine and spruce forest and shade 
trees in the two States. 

The pine-destroying beetle of the Black Hills has been, within the 
past six or eight years, devastating the forests of the Black Hills 
Reserve in South Dakota. It has already killed some 600 million 

265 



266 YEARBOOK OF THE DEPARTMENT OF AGRICULTURE. 

feet of timber, and is threatening a like fate to the remainder. This 
involves not only the destruction of the timber, but also that of the 
great mining and other industries of that region which are dependent 
on the timber supply. 

The records and available evidence show that these three species 
alone have demonstrated their ability, under specially favorable con- 
ditions, to devastate the pine and spruce forests of the entire country. 
Therefore they are worthy of general attention and the most detailed 
investigation. 

The facts already determined by study of the insects and their work 
indicate plainly that most of the forests of the country which are avail- 
able for the application of improved forest methods and systematic 
working plans can usually be protected from this and like dangerous 
enemies at a slight cost. 

The prime requisites for success in combating this class of pests 
are: First, the prompt recognition of the commencement of a trouble; 
second, the determination of the insect causing it; and, third, the 
prompt application of the proper treatment before the depredations 
have spread like a conflagration. 

It is the object of this paper to call attention to what are believed to 
be the worst insect enemies of coniferous forests, also to some of the 
characters of the insects and their work, by which they may be readily 
recognized, and to the peculiar methods of control applicable to each. 

THE SPRUCE-DESTROYING BEETLE 
(Dendroctonus piceapt rda Hopk. ) 

This insect was perhaps the first of its class to claim attention in this 
country, owing to its destructive invasions of the spruce forests of 
New England and New York from 1818 to 1900, as described by Peck. 
Hough, Packard, Fisk, and the present writer. 

DESCRIPTION OF THE VARIOUS STAGES OF THE BEETLE. 

The adult (tig. 23, <i) is a reddish brown to black beetle, varying 
in length from three-sixteenths to four-sixteenths of an inch (4.7 to 
6.0 mm.). The bod} r is sparsely clothed with rather long hairs, and 
has other distinctive characters, as shown in a general way in the 
illustrations. 

The egg is a small, pearly-white object, scarcely to be distinguished 
from those of other bark beetles of the same size. 

The larva (tig. 23, h) when first hatched is a minute white grub, 
which increases in size until it is slightly longer than the beetle, and is 
distinguished from other larva? of the same class by a dark 3-ellowish 
brown space on the upper surface of each of the last two abdominal 
segments. 



Yearbook U. S. Dept. of Agriculture, 1902. 



Plate XXVIII 




Work of the Spruce-destroyinq Beetle. 

[Primary or egg galleries in inner portion of spruce bark, from dead tree. From photograph.] 



SOME INSECT ENEMIES OF CONIFEROUS FORESTS. 



267 



The pupa (tig. 23, c) is nearly white, of the same size and somewhat 
the same form as the adult, but without free legs and wings, and is 
found in oblong cavities in the bark of trees where the broods develop. 

HABITS OF THE ADULT AND LARVA. 

Many pairs of beetles make a simultaneous attack on the lower half 
of the main trunk of medium-sized to large trees. They bore through 
the outer bark to the inner living portion, and through the inner layers 
of the latter they excavate long, irregular longitudinal galleries (PI. 
XXVIII), and along the sides of these, at irregular intervals, numerous 
eggs are closely placed. The eggs soon hatch, and the larva? at once 
commence to feed on the inner bark, and as they increase in size extend 
and enlarge their food burrows in a general transverse but irregular 
course away from the mother galleries (tig. 24, <1). When these young 
or larval forms are full 
grown each excavates a 
cavity or cell at the end 
of its burrow and next 
to the outer corky bark 

The period of devel- 
opment from the egg 
to the matured larva 
varies from two or three 
to nine or ten months, 
depending upon the con- 
dition of the weather 
during growth. With 
the hrst hatched larva? 
in June the period will 
be shorter, while those hatched later in the summer will not com- 
plete their growth until the next spring. Under the climatic condi 
tions prevailing in northwestern Maine, eggs deposited about June 19 
will develop to pupa? by September 1, and to adults by October 4, but 
will not emerge until the next spring. It appears that activity ceases 
about the middle of October, when all stages of the insect may occur 
in the bark of infested trees, where they, with probable exceptions 
of the eggs and pupa?, remain until about the tirst week in June. 
Activity then commences, the matured larva' soon change to pupa>, 
and by the middle of June those that pass the winter in the adult stage 
emerge and commence to excavate galleries and deposit eggs. The 
adults, from hibernating. larvae of different stages, develop and con- 
tinue to emerge from the last of June until the last of August. The 
eggs deposited by the late-developing beetles produce larva? which do 
not complete their development until July or August of the next year, 
and consequently the period from the time the first galleries are exca- 
vated and eggs deposited until the broods of adults emerge is about 




Fig. 23.— Spruce-destroying beetle: a, dorsal view of adult 
beetle; 6, side view of larva; c, dorsal view of pupa — all 
greatly enlarged; d, natural size of beetle. (Original.) 



268 



YEARBOOK OF THE DEPARTMENT OF AGRICULTURE. 



one year. Under different conditions of latitude and altitude these 
(lutes and periods will be different. 

How the tbees are killed. — The numerous primary or egg gal- 
leries penetrate the most vital parts of the tree (the cambium), where 
the principal activity involved in new growth takes place. This 
causes at once a loss of vitality and a weakened resistance. The exca- 




Fig. 24. — Work of the spruce-destroying beetle: o, primary gallery; 6, borings packed in side; 
c, entrance and central burrow through the packed borings; </, larval mines— note how the eggs 
are grouped on the sides. (Original.) 

vation of the primary galleries is immediately followed by the trans- 
verse burrowing operations of the young broods, w T hich rapidly com- 
plete the destruction of all remaining life in the bark. Thus, the tree 
is completely and effectually girdled. This is followed some months 
later by the dying and falling of the leaves and the complete death of 
all parts of the tree. By the time, and even before, the leaves die and 



SOME INSECT ENEMIES OF CONIFEROUS FORESTS. 



269 



fall the new broods of beetles emerge from the bark and migrate in 
swarms to other living trees, which in a like manner are attacked and 
killed. 

Area invaded. — The species extends from New Brunswick to New 
York and westward to the Black Hills of South Dakota; also north- 
ward into Canada. It attacks and kills the Red, Black, and White 
spruces, but only the larger trees. The amount of timber killed by 
it, as indicated by published accounts and the writer's observations, 
has been very great; certainly within the past half century several 
billions of feet of timber have been thus destroyed. 

METHODS OF PREVENTING LOSSES FROM FUTURE DEPREDATIONS. 

A series of experiments conducted during the summer of 1900 and 
again in 1002 resulted in the determination of some important facts 







Fig. 25. — Different methods of girdling trees: a, hack girdled: b, girdled to heartwood; c, hack 
girdled and peeled; d, belt girdled. (From Bulletin Xo. 28, new series, Division of Entomology, 
U.S. Dept.Agr.) 

in the life history of the insect, and in the discoveiy that if living 
spruce trees are hack-girdled (tig. 25) just before the pollen commences 
to fall from the Red Spruce and when it is falling from the birches, 
the conditions, as related both to the flight or swarming period of the 
beetles and to the physiological phenomena of the tree, will be most 
favorable for the attraction of the beetles to such trees; thus, the 
beetles may be made to concentrate their attack upon numerous girdled 
trap trees to be subsequently destroyed during the fall, winter, and 
early spring months, either by the ordinary lumbering operations, 
which insures the removal of the timber from the forests before the 
insects emerge, or by felling the trees and removing the bark from 
the lower two-thirds of the trunk, this method to be supplemented as 
far as possible by the felling and barking of such other trees as are 
found to be infested. Bv this means the number of the beetles may 



270 



YEARBOOK OF THE DEPARTMENT OF AGRICULTURE. 



lie so reduced within large areas as to effectually protect the remaining 
living- timber. It was also determined that the adoption of improved 
forestry methods, which require the intelligent harvesting of the 
matured crop of timber, is doubly beneficial to the forest. These 
methods involve the removal of the trees above 12 inches in diameter, 
which are the only ones attacked by the destructive beetle, and leave 
the younger growth, which is exempt from attack, to produce a future 
.supply of timber. 

THE DESTRUCTIVE PINE-BARK BEETLE. 
(Dendroctonus frontalis Zimm. ) 

The devastation wrought by this beetle in the Virginias and adjoin- 
ing States attracted general attention at the time, and was the subject 
of special investigation by the writer. This insect may be considered 
as one of the most destructive enemies of Southern pine forests. 
Published records of depredations by insects in the pine forests of the 

Southern States within 
the past century indicate 
that it has been the cause 
of repeated widespread 
damage, similar to that 
resulting from its work 
in the Virginias. 





DESCRIPTION OP THE VARIOUS 
STAGES OF THE BEETLE. 



- M 



Fig. 26. — Destructive pine-bark beetle: a, adult beetle, en- 
larged; b, adult, natural size; c, pupa, enlarged, <l, larva, 
enlarged; e, young larva, enlarged; /, egg, enlarged; 
". larva, natural size. (After author, in Bulletin No. 56, 
West Virginia experiment station.) 



The adult (fig. 26, a) is 
a small, rather slender, 
brownish to black beetle, 
varying in length from 
one-twelfth to one-sixth 
of an inch (2.2 to 4.2 mm.). It is distinguished mainly by the very 
broad head and nearly parallel sides of the prothorax. 

The pupa (tig. 26, c) also differs in having a proportionately larger 
prothorax, with sides less constricted in front. 

The larva (fig. 26, d) is strikingly different from that of the spruce- 
destroying beetle in the globular form of the curled-up, freshly 
hatched individuals (fig. 26, e) and in the much enlarged prothoracic 
segments; also in the last abdominal segments being truncated and 
unarmed. 



SOME INSECT ENEMIES OF CONIFEROUS FORESTS. 271 



HABITS OF THE ADULT AND LARVA. 



In this species the adults normally invade the bark of the middle 
trunk of medium to large pine and spruce trees and the middle to 



Fig. 27.— Work of destructive pine-bark beetle. a, a, a, a, characteristic forms of primary galleries; 
b, normal lorms of larval mines, c, abnormal forms of larval mines— all slightly reduced. 
(Original.) 

lower portion of the smaller ones. The habit of attack and methods 
of excavating galleries is similar to that of the spruce beetle, but the 



272 YEARBOOK OF THE DEPARTMENT OF AGRICULTURE. 

character of the primary gallery is strikingly different. Instead of 
extending nearly straight up and down the tree it extends from the 
entrance in a transverse and tortuous course through the inner bark 
(fig. 27). Those of different pairs of beetles frequently cross each 
other, so that the many primary galleries, independent of the larval 
mines, serve to completely girdle the tree and kill the bark, thus 
causing a much more rapid death of the bark and foliage than when 
the primary galleries, like those of the spruce beetle and the pine 
beetle of the Black Hills, extend parallel with the elongated sieve 
tissues and cells through which the life-supporting and wood-forming 
liquids pass. The larval burrows are also quite different, being nor- 
mally very short and broad. The pupal cells are usually excavated in 
the outer dry bark, while those of the spruce beetle are normally in 
the outer portion of the inner bark. 

The time required for the development of a brood varies greatly 
with the season, latitude, altitude, etc. In West Virginia, at a 
medium altitude of 1,000 feet above tide, there appear to be two 
broods, one emerging in August and the other in September. 

The winter is passed in the adult stage and in all stages of the larva, 
with possibly a few eggs and pupa?. 

How the trees are killed. — The trees are killed by the girdling 
effect of the primary galleries in the bark of the middle portion of the 
trunk — which, as has been demonstrated, is the most vital part, or at 
least has less power of resisting injuries than the lower portion and 
base. Instead of the leaves of infested trees remaining green until 
the next season, as is the case with trees infested by the spruce beetle 
and the pine beetle of the Black Hills, all except those attacked late 
in the season commence to fade in a few weeks after the attack; so 
that trees attacked about the middle of July will be entirely dead and 
the leaves brown by the first of November or earlier, when all of the 
broods of beetles will have emerged. The trees infested with broods 
at the beginning of winter may present in the foliage all stages of 
color, from yellowish to perfect green. 

Kinds of trees attacked.— This beetle is known to attack the 
Shortleaved Yellow Pine, Pitch Pine, Scrub or Virginia Pine, Table 
Mountain Pine, and White Pine, and recent observation indicates that 
the Lobloll} T and Longleaf pines are also attacked and killed by it. 
It also attacks and kills the native Red Spruce and the introduced 
Norway Spruce. 

Distribution and area of principal depredations. — This species 
with its work has been observed by the writer in West Virginia, Vir- 
ginia, Maryland, North Carolina, South Carolina, Texas, and the 
District of Columbia, and has been recorded by other writers from 
Georgia to Lake Superior, Florida, Colorado, Arizona, and California. 
The Western forms heretofore associated with it have, however, been 



SOME INSECT ENEMIES OF CONIFEROUS FORESTS. 273 

recently found by the writer to represent several distinct species. 
The destructive invasion in 1890-1892, as determined by the writer, 
extended from the western border of West Virginia through Mary- 
land, Virginia, and the District of Columbia, and northward into 
southern Pennsylvania and southward into western North Carolina, 
an area of over To, 000 square miles, in which a vast amount of pine 
and spruce was killed by it. In many places in West Virginia and 
Virginia nearly all. of the pine of all sizes, from a few inches in diam- 
eter to the largest trees, was killed on hundreds and even thousands of 
acres, while shade and ornamental trees within the same area suffered 
the same as those in the forest. The total destruction of the pine and 
spruce of the entire area was threatened, but the severe freeze of 
December, 1892, and January, 1893, together with natural enemies, 
exterminated the pest or so reduced its numbers that no more timber 
died after the summer of 1893, since when to the date of the present 
writing not a living example of the beetles has been found north of 
North Carolina. 

PROBABLE BEGINNING OF A NEW INVASION IN THE SOUTH. 

Recent investigation in the Southern Appalachian region has demon- 
strated the fact that the insect is living there, and that scattering- 
clumps of trees are being killed by it as they were in the early stages 
of the great invasion of 1890-1892. 

EVIDENCE OF AN OLD INVASION IN TEXAS. 

It has also been recently determined that a great amount of timber 
died in the Longleaf Pine region of eastern Texas between 1882 and 
1885, which, as evidenced by the dead beetles found preserved in the 
pitch and the characteristic galleries in the bark from the old dead 
trees, was probably due to the presence of this insect in destructive 
numbers at that time. 

Knowing what devastations were wrought by this beetle in the Vir- 
ginias within two or three years and what it evidently did in Texas 
within about the same length of time, we conclude that during a series 
of years of especially favorable conditions it is capable of devastating- 
the entire pine and spruce forests of the South. Therefore, it presents, 
in the writer's opinion, the most important forest insect problem in 
this country, and one which demands immediate action to prevent a 
possible widespread invasion, which would be a real calamity to the 
South. 

METHODS OF PREVENTING DESTRUCTIVE INVASIONS. 

From what has been learned of the habits of this insect, it is known 
that it passes the winter in different stages in the inner and outer bark 
of trees attacked by the adult beetle in September to November. The 
trees so infested may be detected by the faded and yellowish foliage 



274 YEAKBOOK OF THE DEPARTMENT OF AGRICULTURE. 

of the (tying trees, or by the pitch tubes and borings in the loose outer 
bark and at the bases of such infested trees as show no change in the 
foliage from the normal green. The principal infestation is in the 
bark of the main trunk of medium to large trees, and among the lower 
branches to the bases of small trees and saplings. 

In order to effectually destroy the insect it is only necessary to fell 
the larger trees, remove the bark from the trunks, and burn it. It is 
entirely unnecessary to burn or otherwise destroy any part of the 
wood, because the destructive beetle does not enter the wood and rarely 
breeds in the bark of the tops and branches, but with this particular 
species it is necessary to burn the bark removed in the winter, 
because the matured larvae, pupae, and adults pass the winter in the 
outer dry bark, where they would otherwise survive and emerge in 
the spring to attack other trees. 

The infested small trees may be felled and barked or burned, or the 
bark removed from the infested parts by means of suitable barking 
tools, as is sometimes done in European forests. 

The summer broods of the insect can also be destroyed by felling 
and barking recently infested trees. 

As an example of what ma} T be accomplished by the cutting and 
peeling process, Mr. G. H. Warner, in March, 1902, cut the infested 
trees in four different widely separated clumps of from 1 to 2 acres 
each in the forest of the William Gillette place, near Tryon, N. C, and 
removed the bark and burned it. Examination of this place b} T the 
writer in July, and of the vicinity in November, of the same year, 
indicated that a sufficient number of the beetles and their broods had 
been thus killed to protect a very large area from further attack. At 
least no recently attacked trees were observed on the place or in the 
immediate vicinity. 

It is well known by people in the South that if a pine tree standing 
in the midst of a healthy forest is girdled, struck by lightning, felled 
by ax or storm, or otherwise seriously injured, during the middle of 
the summer, it will cause the death of the other pine trees immediately 
surrounding it, over areas varying from a few rods to several acres. 
This is due to the fact that the destructive beetle breeds in such trees, 
and emerges in sufficient numbers to attack and kill the living timber. 
Such trees should be felled and have the bark removed, whenever 
practicable, soon after the leaves begin to fade. 

It must be remembered that the bark and wood of trees dying or 
dead from the work of the destructive beetle are always infested by 
many other kinds of bark-beetles and wood-boring beetles, as well as 
bark-grubs and wood-boring grubs, the latter known locally as "bore 
worms " or " sawyers." Therefore, these must not be confused with the 
real destroyer. The destructive beetle and its characteristic galleries 
in the bark can be easily distinguished from the secondary enemies by 



SOME INSECT ENEMIES OF CONIFEROUS FORESTS. 275 

comparing- them with fig. 24, d, and descriptions. Tt is a common mis- 
take by the unentomological observer to conclude that some of these 
secondary enemies, especially the sawyer, are to blame for the death 

of the trees. 

TRAPPING THE BEETLE AND ITS BROODS. 

Some facts in the habits of the beetle in the present infested region 
recently determined by the writer indicate clearly that it can be easily 
trapped during- the summer and destroyed by means of the well-known 
method of girdled and felled trap trees. It \v;is found that the adults 
are attracted to storm-felled and otherwise felled and injured trees, 
and that such trees, if neglected, form a nucleus for the rapid multi- 
plication of the insect and its spread to healthy standing timber. 
Therefore, if felled and girdled trees are provided at the proper time, 
so that the beetles will be attracted to them at the period of their 
greatest flight, they will attack such trees in preference to the living 
uninjured ones. Then, after they have entered the inner bark and the 
broods are partially developed, that is, before they have entered the 
outer bark, it will only be necessary to remove the bark to effectually 
destroy them, and thus protect the healthy timber. If, however, the 
removal of the bark is neglected until the broods have entered the 
outer dry portion, it will be necessary to burn it as soon as it is 
removed. 

THE PINE-DESTEOYING BEETLE OF THE BLACK HILLS. 
(Dendroctonus ponderosse Hopk.) 

This beetle is now causing widespread destruction to the Bull Pine 
in the Black Hills Forest Reserve and is the subject of detailed investi- 
gation by the Department. The fact that it may spread through the 
entire Rocky Mountain region and cause general destruction of the 
pine and spruce renders it an insect of special interest and importance. 

DESCRIPTION OF THE BEETLE AND ITS WORK. 

The beetle (tig. 28). — The fully matured adult is a stout dark- 
brown or black beetle, individuals of which vary in length from about 
one-sixth to one-fourth of an inch (4 to 7 mm.). It differs from 
the spruce-destroying beetle, with which it agrees in size, mainly in 
the absence of long hairs on the prothorax and elytra; and from the 
destructive pine-bark beetle in its much larger size, also in other 
specific characters which would require a technical description. 

The egg differs but slightly from that of the spruce beetle. 

The larva (tig. 29) resembles that of D. frontalis, but differs in 
being of much larger size and in having the prothoracic segments 
much less enlarged. 

The PurA (fig. 30) is scarcely to be distinguished by the ordinary 
observer from that of the spruce beetle. 
26084—03 2 



276 



YEARBOOK OF THE DEPARTMENT OF AGRICULTURE. 




Fig. 28. — The pine-destroying beetle 
of the Black Hills: a, adult beetle, 
enlarged; b, adult beetle, natural 
size. (Original.) 



Characteristic features of the work of the beetle and 
larva.— The attack of this beetle on living- trees and the general fea- 
tures of its operation beneath the bark and method of killing- the trees 
is similar to that of the two preceding; but it differs in the time of 
flight, character of galleries (fig. 31), and other minor details. It com- 
mences to emerge and liy during the last 
half of Jul}*, and the adults, which subse- 
quently develop from different stages of 
the hibernating broods, continue to emerge 
until in September. The main swarm, 
however, emerges during the last half of 
July and the first half of August and attack 
the living timber. They settle on widely 
separated clumps of trees, or invade the 
living timber adjoining that from which 
they emerged. The number of trees in- 
vaded in one locality varies 
from two or three to many 
hundreds, or even thou- 
sands. Each tree is attacked 
by a great number of pairs 
of beetles, which enter the bark from near the base up 
to about the middle of the trunk of medium-sized to 
large trees, and on the lower portion of the main stem 
of the smaller ones. They then begin to excavate the 
entrance burrows, which are usu- 
ally in crevices hidden by the flakes 
of the dry bark. The reddish saw- 
dust-like borings thus produced fall 
to the ground or lodge in the flaky 
bark or the outer part of the trunk. 
When the beetles enter the inner bark, or bast, the 
tree commences to exert its resistance to the enemy 
by throwing out pitch to fill and heal the fresh 
wounds in the living tissue (fig. 32). During the 
earlier attack the borings and pitch are pushed out 
by the beetles and formed into pitch tubes at the 
mouth of the entrance burrows; while later, in 
August, when the tree is apparently less able to 
exert resistance, pitch tubes are not necessarily 
formed, but the borings lodge in the loose bark and around the base 
of the tree. 

The inner bark is entered obliquely, or transversely to the cambium 
or outer portion of the w r ood, where a broadened cavity is excavated 
for the accommodation and temporary occupation of the parent beetle 





Fig. 30.— Pupa of 
the pine-destroy- 
ing beetle of the 
Black Hills. 



Fig. 29.— Larva of the 
pine-destroying hectic 
of the Black Hills. 



SOME INSECT ENEMIES OF CONIFEROUS FORESTS. 



277 



until the principal flow of pitch is exhausted. The galleiy is then 
extended transversely or subtransversely for a short distance, seldom 
more than an inch or two, and then longitudinally up or down the 
tree, varying in length from a few inches to over 2 feet (tig. 31). 
As soon as the gallery has been extended 1 or 2 inches from the 
entrance and basal cavity, small notches are excavated in the sides of 
the gallery, in each of which an egg is deposited, and so on until the 
gallery is completed. 
As the eggs are depos- 
ited, the borings, in- 
stead of being thrown 
out at the entrance, 
are closely packed in 
the entrance burrow, 
basal cavity, and gal- 
lery, except near the 
farther end, which is 
kept open and en- 
larged or extended to 
one side or the other, 
as it is occupied by the 
parent beetles, after 
the work of construct- 
ing the egg galleries is 
completed, until the}" 
die. 

The bark of an in- 
fested tree is usually 
occupied b} T one of 
these primary galler- 
ies every 1 to 6 inches 
of the circumference, 
from near the base to 
near the middle of the 
trunk; therefore they 
effectually check the normal movement of the sap. and the larval mines, 
which radiate from the primary gallery, destroy the intervening bark, 
and complete the girdling process. The larval mines are similar in 
character to those of D. frontalis, and quite different from those of 
D. p/ceaperda, as will be noted by comparing tigs. 24 and 31. The 
larva? undergo their transformation to the pupa in cells excavated in 
the inner bark at the end of the larval gallery. 

Kinds of trees attacked. — So far as has been observed, this beetle 
attacks and kills the Bull Pine {Pi mix ponderosa) and the White Spruce 
{Picea canadensis), but shows a decided preference for the pine. 




Fig. 31. — Work of the pine-destroying beetle of the Black Hills: 
a, a, a, entrance and basal chamber: h, ventilating holes in roof 
of gallery; r, termination of gallery (larval mines extending 
from each side of primary galleries) — all much reduced. (After 
author, in Bulletin No. 32, new series, Division of Entomology.) 



278 



YEARBOOK OF THE DEPARTMENT OF AGRICULTURE. 



Distribution of the species and extent of its depredations. — 
The beetle has been reported by Professor Gillette from central Colo- 
rado, which indicates that it may be found throughout the central 
Rocky Mountain region; but, so far as determined, it has not proved 
so destructive anywhere else as in the Black Hills Reserve, where in 

the past six years from 400 
to 600 million feet of timber, 
according to various esti- 
mates, have been killed by it. 
Recent investigations in- 
dicate that at least 80 per 
cent of the merchantable 
timber west of Spearfish 
Creek to the Wyoming line 
has been killed. There is 
a decided increase in the 
spread of the depredations 
by the beetle eastward and 
southward. It is threaten- 
ing the large areas of healthy 
timber in the southern hills, 
and unless checked it will 
doubtless extend its destruc- 
tive work in that direction, 
as it has northwestward. 

The Black Hills Forest Re- 
serve is recognized as one of 
the most important in the 
country, especially in its im- 
mediate relations to the sup- 
port of great mining indus- 
tries. The annual product 
of gold mined in the Black 
Hills amounts to about 
$10,000,000. The methods of 
mining require the use of 
some 20 million feet of mine 
timbers each year. The 
process of extracting the 
gold from the ore requires 
thousands of cords of wood for fuel. The average low grade of the 
ore and the expensive processes of mining and reduction require that 
the supply of such timberbe readily accessible and procurable at a low 
price. The cost of transportation of timber from other reserves or 
other Western forests would prohibit its use. Therefore, as stated b} r 
the superintendent of one of the principal mines, "the mining interests 




Fig. 32.— Work of the pine-destroying beetle of the Black 
Hills: a, piti h tubes on surface of bark, much reduced; 
b, same, two-thirds natural size. (Original.) 



SOME INSECT ENEMIES OF CONIFEROUS FORESTS. 279 

of South Dakota are dependent upon the limited timber resources of 
the Black Hills.* 1 The d\ T ing of the timber is threatening the life of the 
mining industry and of all the many other interests which depend upon it. 

CHARACTERISTIC FEATURES OF THE INFESTED AND DEAD TIMBER. 

The characteristic features which are of importance to the reserve 
officials, lumbermen, and residents in recognizing the presence and 
work of the pine-destroying beetle arc as follows: 

Borings and pitch tubes. — The first indication of attack is the red 
dust or borings lodged in the loose outer bark or scattered upon the 
ground about the base of the tree. The next and a more conspicuous 
evidence is the presence of numerous small masses of pitch, or 
so-called pitch tubes, on the outer bark at the mouth of the entrance 
burrows (fig. 32). 

Appearance of the leaves. — The leaves of the trees attacked by 
the beetle in July to September in any year, for example, in 1899, 
retain their normal green until May of the next year, that is, till 1900. 
Then the leaves of the lower branches begin to fade and gradually 
change to yellowish. This condition rapidly spreads toward the top, 
until all are dead by the first or middle of August. The trees in this 
stage are designated by lumbermen as "sorrel tops." By the time, 
and often before, all the leaves are dead the broods of beetles have 
emerged and entered the living timber. After this the recently dead 
and vacated trees are of no further importance as sources of danger 
as breeding places for the pine-destroying beetle. 

By the summer of the next year (1901) the leaves change to a 
reddish brown and commence to fall. The trees in this stage are 
referred to as " red tops.** 

By the summer of the year after that (1902) all of the leaves have 
fallen, and in this stage the trees are referred to as "black tops. *' 
Still later (1903-1901) most of the tops will break off. They are then 
called "broken tops.'* 

The bark of the lower half or two-thirds of the newly infested trees 
usually dies within a few weeks after the primary galleries are com- 
pleted, or by the middle to the last of September of the year in which 
the attack is made; and when thoroughly infested the bark may then 
be readily separated from the wood. The sapwood will then be 
found chanoed from the natural color to a bluish hue." 



"Bluing of the wood.— According to information from Dr. Von Schrenk (who 
has made detailed investigations of the deterioration and decay of the wood of the 
beetle-killed trees), the bluing of the sapwood of the infested trees is due to a 
fungus which enters the burrows in the bark made by bark beetles and those in the 
wood made by timber beetles. The writer has determined that this blue wood 
trouble is not only associated with the recently excavated galleries of the destructive 
beetle, but also with those of the numerous other bark-boring and wood-boring 
beetles, which follow the attack of the former and excavate their primary galleries 
in the living bark and sapwood. 



280 yearbook of the department of agriculture. 

Evidence of the work of the beetle on the surface of the 
wood. — The peculiar grooves and marks in the surface of the wood 
made by the pine-destroying beetle during the process of excavating 
the primary or ogg galleries, as seen on the barked surface of dead 
trees, sawlogs, railroad ties, mine timbers, etc., are always unmistaka- 
ble evidence of its work (PI. XXIX). While there are many other 
kinds of bark beetles and bark-boring grubs which follow the attack 
of the destructive beetle, and excavate each its peculiar kind of gallery 
or groove on the wood, none of these marks can be mistaken for the 
peculiar longitudinal grooves made by the destructive species." 

METHODS OF COMBATING THE TEST. 

Experiments with girdled trees.— Experiments with girdled and 
felled trees, to determine whether or not the trap-tree method would 
be practicable in dealing with the pine-destroying beetle in the Black 
Hills Reserve, seem to demonstrate, among many other important 
facts in the life history and habits of the beetle, that while some of 
the girdled as well as felled trees were infested, the near-by living and 
uninjured trees were equally attacked. Therefore, it would seem from 
the results of this season's work that the trap-tree method, which is so 
admirably adapted for the control of similar troubles by other kinds 
of bark beetles in this country and Europe, is not adapted to the con- 
ditions attending the Black Hills trouble. This is probably due to 
some peculiar characteristic of the species or variet} T of pine involved. 

Further experiments, however, may show that while none of the 
several methods and dates of girdling and felling the trees are available 
in checking or controlling the insect in its present magnitude, some 
one or more of them may prove to be adapted to the prevention of its 
recurrence after it has once been brought under control b} T other 
methods. 

Cutting and barking the infested trees to destroy the young 
broods. — After a thorough study of the prevailing conditions in the 
Black Hills Reserve, both as regards the extent of the present depre- 
dations, the peculiar habit of the depredator, and the relative abun- 
dance of the several kinds of natural enemies which prey upon the 
parent beetles and different stages of its broods, the writer is con- 
vinced, as stated in his recommendations, that in order to destroy a 
sufficient number of the young stages of the beetles to render any 
special service toward checking or ending the depredations, it is neces- 
sary that the beetle-infested trees in all of the principal areas of new 
infestation throughout the reserve be cut and the bark removed from 



« For illustrated forms of galleries made by secondary enemies of the trees, see 
" Insect enemies of the pine in the Black Hills Forest Reserve," Bulletin No. 32, 
new series, Division of Entomology, U. S. Dept. Agr. 



Yearbook U. S. Dept. of Agriculture, 1902. 



Plate XXIX. 





SOME INSECT ENEMIES OF CONIFEROUS FORESTS. 281 

the infested parts of the trunks between the 1st of September (1902) 
and the 1st of May (1903). 

It is also evident that if these principal areas of newly infested timber 
in the western and southern hills are cut over, the natural enemies, 
including- insects and birds, will be able to so reduce the numbers of 
the beetles left in the scattering- uncut infested trees as to prevent the 
continuation of their destructive ravages, and that the pest will thus 
be kept under complete control, especially if the future management 
of the reserve shall provide for the cutting of such newly infested 
clumps of trees as from time to time may be found. Recommenda- 
tions to this effect have been submitted by the writer to the Bureau of 
Forestry and to the General Land Office for consideration in their 
future management of the forest and administration of the reserve. 

OTHER DESTRUCTIVE SPECIES OF DENDROCTONUS. 

The other species of the genus Dendroctonus which have been 
found by the writer to be specially destructive, but which for lack of 
space can not be described in this article, are four undescribed and 
two described species. One is destructive to the Silver or Mountain 
^'hite Pine, in Montana and Idaho. Anothet- destroys the Red Fir 
from Idaho to western Washington and Oregon. One of the described 
species (Dendroctonus brevicomds Lee.) kills the Western Yellow Pine 
in California and Oregon to western Idaho. The other described 
species (I), approsrimatits Dietz), together with two undescribed 
species, attacks and kills the Bull Pine in northern Arizona. 

With a few modifications to suit local conditions and varying 
features in the habits of these species, the same recommendations 
for dealing with troubles caused by D. piceaperda, D. frontalis, and 
D. ponderosse may be adopted. 

SUMMARY. 

The principal destructive enemies of coniferous forests in this 
country belong to the Dendroctonus genus of bark beetles. 

The spruce-destroying beetle has killed billions of feet of spruce 
timber in the Northern spruce forests in the past sevent}'-live or 
eighty years. It can be controlled by cutting the infested trees dur- 
ing the fall, winter, or early spring months, and removing the bark 
from the infested parts of the main trunks. It can also be attracted 
to trap trees hack girdled during the last week in May or first week in 
June, and subsequently destroyed by felling them and removing the 
bark in the summer after the broods are partially developed, or during 
the following winter. 

The destructive pine bark-beetle destroyed millions of dollars 
worth of pine and spruce forest and shade trees in an area including 



282 YEARBOOK OF THE DEPARTMENT OF AGRICULTURE. 

West Virginia, Virginia, Maryland, and the District of Columbia 
between 1890 and 1892. 

The natural home of the species is evidently in the Southern Appa- 
lachian region, where it is now at work, and is a menace, not only to 
the pine and spruce of that region, but to the coniferous forests of the 
entire Southern and Eastern United States. 

If taken in time, this pest can be controlled by felling the infested 
trees and removing the bark from the infested parts of the trunks and 
burning it; also by means of trap trees. 

The fine-destroying beetle of the Black Hills has killed 
many hundreds of millions of feet of pine timber in the Black Hills 
Forest Reserve within the past six or seven years, and is at the pres- 
ent time threatening the destruction of the remaining timber of the 
reserve, together with the great mining and other industries which 
depend upon the forest resources. 

In order to check the ravages of this beetle and protect the remain- 
ing living timber, it is necessary to cut and bark all of the principal 
clumps and bodies, or an aggregate of at least 50 per cent of trees 
which were attacked by the beetle during the summer of 1902 — a 
remedy which has been recommended by the writer and has been 
adopted by the General Land Office to be applied so far as it is possible 
and practicable to do so. 

general recommendations. 

It is of the greatest importance that the commencement of depre- 
dations similar to those described in this article, as indicated by isolated 
clumps of dying trees in the pine or spruce forests of any section of 
the country, should be reported to the Department of Agriculture as 
soon as discovered, in order that the matter may be investigated and 
prompt information given on tne proper course to pursue in each par- 
ticular case to prevent the widespread depredations which may follow 
neglect. 



LIBRARY OF CONGRESS 



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